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ISL29011 View Datasheet(PDF) - Intersil

Part NameDescriptionManufacturer
ISL29011 Digital Ambient Light Sensor and Proximity Sensor with Interrupt Function Intersil
Intersil Intersil
ISL29011 Datasheet PDF : 16 Pages
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ISL29011
Registers 06 and 07 hex set the high (HI) threshold for the
interrupt pin and the interrupt flag. 06 hex is the LSB and 07
hex is the MSB. By default, the Interrupt threshold HI is FF
hex for both LSB and MSB.
Test Register (08 hex)
Register 8 is a reserved register that holds 00h during
normal operation.
Calculating Lux
The ISL29011’s ADC output codes, DATA, are directly
proportional to lux in the ambient light sensing.
Ecal = α × DATA
(EQ. 1)
Here, Ecal is the calculated lux reading. The constant α is
determined by the Full Scale Range and the ADC’s
maximum output counts. The constant is independent on the
light sources (fluorescent, incandescent and sunlight)
because of the light sources’ IR component is removed
during the light signal process. The constant can also be
viewed as the sensitivity: the smallest lux measurement the
device can measure as shown in Equation 2.
α
=
-R-----a----n---g----e----(--k----)-
Countmax
(EQ. 2)
Here, Range(k) is defined in Table 9. Countmax is the
maximum output counts from the ADC.
The transfer function used for n-bit ADC becomes
Equation 3:
Ecal
=
R-----a----n----g----e----(--k----) × DATA
2n
(EQ. 3)
Here, n = 4, 8, 12 or 16. This is the number of ADC bits
programmed in the command register. 2n represents the
maximum number of counts possible from the ADC output.
Data is the ADC output stored in the data registers (02 hex
and 03 hex).
Integration and Conversion Time
The ADC resolution and fOSC determines the integration
time, tint as shown in Equation 4.
tint
=
2n
×
------1-------
fOSC
=
2n × 7----2---5----k---H--R---z--E---×X----T-4---9---9----k----Ω--
(EQ. 4)
where n is the number of bits of resolution and n = 4, 8, 12 or
16. 2n, therefore, is the number of clock cycles. n can be
programmed at the command register 01(hex) bits 3 and 2.
TABLE 11. INTEGRATION TIME OF n-BIT ADC
REXT n = 16-BIT n = 12-BIT n = 8-BIT
(kΩ)
(ms)
(ms)
(µs)
n = 4-BIT
(µs)
250
45
2.812
175.5
10.8µs
499**
90
5.63
351
21.6µs
**Recommended REXT resistor value
External Scaling Resistor REXT for fOSC and Range
The ISL29011 uses an external resistor REXT to fix its
internal oscillator frequency, fOSC and the light sensing
range, Range. fOSC and Range are inversely proportional to
REXT. For user simplicity, the proportionality constant is
referenced to 499kΩ as shown in Equations 5 and 6:
Range
=
-4---9---9----k---Ω---
REXT
×
R
a
n
ge
(
k
)
(EQ. 5)
fOSC
=
4----9---9----k---Ω---
REXT
×
725
k
H
z
(EQ. 6)
Noise Rejection
In general, integrating type ADC’s have excellent
noise-rejection characteristics for periodic noise sources
whose frequency is an integer multiple of the conversion
rate. For instance, a 60Hz AC unwanted signal’s sum from
0ms to k*16.66ms (k = 1,2...ki) is zero. Similarly, setting the
device’s integration time to be an integer multiple of the
periodic noise signal, greatly improves the light sensor
output signal in the presence of noise.
ADC Output in IR Sensing
The ISL29011’s ADC output codes, DATA, are directly
proportional to the IR intensity received in the IR sensing.
DATAIR = β × EIR
(EQ. 7)
Here, EIR is the received IR intensity. The constant β
changes with the spectrum of background IR noise like
sunlight and incandescent light. The β also changes with the
ADC’s range and resolution selections.
ADC Output in Proximity Sensing
In the proximity sensing, the ADC output codes, DATA, are
directly proportional to the total IR intensity from the
background IR noise and from the IR LED driven by the
ISL29011.
DATAPROX = β × EIR + γ × ELED
(EQ. 8)
Here, β and EIR have the same meanings as in Equation 7.
The constant γ depends on the spectrum of the used IR LED
and the ADC’s range and resolution selections. ELED is the
IR intensity which is emitted from the IR LED and reflected
by a specific objector to the ISL29011. ELED depends on the
current to the IR LED and the surface of the object. ELED
decreases with the square of the distance between the
object and the sensor.
If background IR noise is small, EIR can be neglected, and
the ADC output directly decreases with the distance. If there
is significant background IR noise, ISL29011 offers two
schemes to reduce the effect. The first way is do a proximity
sensing using Scheme 0, immediately followed by an IR
sensing. The differential reading of ADC outputs from the
proximity and IR sensing will then reduce the effect of
background IR noise and directly decrease with the distance
between the object and the sensor. The second way is to do
10
FN6467.3
February 4, 2010
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